Messrs. George Whitefield Betts, Jr., of New York City, and Edmund B. Whitcomb, of Toledo, Ohio, for respondents.

Mr. Justice ROBERTS delivered the opinion of the Court.

The courts below have held valid and infringed certain claims of three patents 1 granted to Genzo Shimadzu, a citizen and resident of Japan. The earliest is for a method of forming a finely divided and, consequently, more chemically reactive, lead powder. The second is for a method or process of manufacturing a fine powder composed of lead suboxide and metallic lead and for the product of
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the process. The third is for an apparatus for the continuous production of lead oxides in the form of a dry fine powder. Such powder is useful in the manufacture of plates for storage batteries.

The bill was filed by the respondents as patentee and exclusive licensee. The answer denied that Shimadzu was the first inventor; asserted knowledge and use of the invention by the petitioner in the United States more than two years prior to the dates of the applications; and pleaded that earlier patents procured by Shimadzu in Japan avoided the United States patents as the former were for the same inventions and each was granted more than a year prior to the filing of the corresponding application in this country. The case was tried, the District Court found the facts, stated its conclusions, and entered a decree for the respondents,2 which the Circuit Court of Appeals affirmed. 3 The petitioner sought certiorari alleging that the case presents three questions, one which should be settled by this court and two which were decided below contrary to our adjudications.

The questions are: In an infringement suit by the owner of a patent for an invention, made but not patented or published abroad, to restrain an innocent use, the inception of which antedates the application for patent, may the plaintiff prove that his actual date of invention was earlier than the commencement of the asserted infringing use? Is the delay of the patentee in this case in applying for patent a bar to relief for alleged infringement? Does commercial use of the patented process and apparatus in the alleged infringer's plant for more than two years prior to the application for patent preclude redress?
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No controversy of fact is involved as the petitioner concedes it must accept the concurrent findings of the courts below.
4
The relevant facts lie within a narrow compass.

The inventions which are the basis of the patents were conceived by Shimadzu and reduced to practise in Japan not later than August 1919. He did not disclose the inventions to anyone in the United States before he applied for United States patents. Application was presented for No. 1,584, 149 on January 30, 1922; for No. 1,584,150 on July 14, 1923; and for No. 1, 896,020 on April 27, 1926. The inventions were not patented or described in a printed publication in this or any foreign country prior to the filing of the applications. The petitioner, without knowledge of Shimadzu's inventions, began the use of a machine, which involved both the method and the apparatus of the patents, at Philadelphia, Pennsylvania, early in 1921 and attained commercial production in June 1921. Over the objection of the petitioner the respondents were permitted by testimony, and by the introduction of contemporaneous drawings and note books, to carry the date of invention back to August 1919, and the courts below fixed that as the date of invention and reduction to practise in Japan.

First. The petitioner asserts that R.S. 4886, 4887, and 4923,5 considered together, require one who has made
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an invention abroad to take as his date of invention the date of his application in the United States unless, prior thereto, the invention has been communicated and described to someone in this country, or has been patented abroad. The respondents insist that the sections have no such force. They say that where the alleged infringer is not acting under the supposed protection of a prior patent, but is using an unpatented process or device, the holder of a patent for a foreign invention, like the holder of one for an invention made here, may show novelty by proving that his invention antedated his application and the infringing use.

The solution of the issue requires examination of two of the sections in the light of their development from earlier patent statutes.

R.S. 4886, as it stood when the patents were granted,6 was:

'Any person who has invented or discovered any new and useful art, machine, manufacture, or composition of matter, or any new and useful improvements thereof, not known or used by others (in this country), ( before his invention or discovery thereof), and not patented or described in any printed publication in this or any foreign country, before his invention or discovery thereof, (or more than two years prior to his application), and not in public use or on sale (in this country) for more than two years prior to his application, unless the same is proved to have been abandoned, may, upon payment of the fees required by law, and other due proceeding had, obtain a patent therefor.'

The legislative history of the section may be briefly outlined. The Patent Act of 17907 authorized the grant
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of a patent to 'any person or persons' who made an invention 'not before known or used.' The succeeding Act of 17938 confined the privilege to 'a citizen or citizens of the United States', but the Act of 18009 conferred it on any alien who, at the time of his application, had resided for two years within the United States. By the Act of 183610 it was provided that a patent might be obtained by 'any person or persons.' The Act of 1870,11 which was carried into the Revised Statutes, added the words 'in this country' as they appear in the first bracket in the foregoing quotation. The Act of 189712 added the three other bracketed clauses.

The requirement of the Act of 1790 was that the discovery be 'not before known or used.' The Act of 1793 amended this to read 'not known or used before the application.' The Act of 1800 altered the provision so that the petitioner had to swear that his invention had not 'been known or used either in this or any foreign country.' The Act of 1836 changed the knowledge and use clause to read 'not known or used by others before his or their discovery or invention thereof.'

These successive alterations throw into relief the fact that the section makes the criterion of novelty the same whether the invention was conceived abroad or in this country. The test is whether the invention was 'known or used by others in this country, before his invention or discovery thereof.' The elements which preclude patentability are a patent, or a description in a printed publication in this or any foreign country, which antedates the invention or discovery of the applicant.
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None of the statutes has ever embodied as an element the place of invention or discovery, but the change effected by the Act of 1836, and carried forward in all succeeding statutes, is the fixation of the actual date of the inventive act as the date prior to which the invention must have been known or used to justify denial of a patent for want of novelty. The omission of any limitation as to the place of invention or discovery precludes a ruling imposing such a limitation, especially so since the Act of 1870 expressly limited the area of prior knowledge or use to this country.

The provisions of R.S. 4886 which affect the question are not modified by R.S. 4887, the purpose of which is to permit the filing of applications for the same invention in foreign countries and in the United States. It derives from Section 25 of the Act of 1870.13

The second paragraph of the section, which was added by the Act of 190314 to comply with reciprocal agreements with foreign countries, gives the same force and effect to the filing of an application in a foreign country as it would have if filed here on the date on which the application for patent was first filed in the foreign country, provided that the domestic application is filed within twelve months of the foreign filing date. The last sentence of the paragraph expressly preserves the bars of more than two years' prior patenting, description in a printed publication before the filing of application in this country, and public use, more than two years before such filing. But the section does not contain any provision which precludes proof of facts respecting the actual date of invention in a foreign country to overcome the prior knowledge or use bar of 4886.

The petitioner also relies upon R.S. 4923, 35 U.S.C.A. 72, which provides that if the patentee, at the time of his application,
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believed himself the original or first inventor, his patent shall not be refused or held void by reason of the invention having been known or used in a foreign country, before his invention or discovery, if it had not been patented or described in a printed publication. The effect of this section is that in an interference between two applicants for United States patent, or in an infringement suit where the alleged infringer relies upon a United States patent, the application and patent for the domestic invention shall have priority despite earlier foreign knowledge and use not evidenced by a prior patent or a description in a printed publication.

The section, on its face, is without application where the litigation is between the patentee of a foreign invention, or his assignee, and an alleged infringer who defends only in virtue of prior knowledge or use not covered by a patent.

While this court has never been called upon to decide the precise question presented, the lower federal courts have refused to extend 4923 to such a case. They have held that 4886 does not limit the plaintiff to the date of application in this country but that he may prove the invention was in fact made at an earlier date, as could the owner of an invention made in the United States.
15

There is force in the petitioner's argument that the distinction seems illogical. Thus, if a diligent domestic inventor applies, in good faith believing himself to be the first inventor, Section 4923 assures him a patent and gives it priority, despite prior foreign use, even though that use is evidenced by a patent applied for after the invention made in this country. The foreign applicant or patentee
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cannot carry the date of his invention back of the date of application in this country, as the holder of a later patent for an invention made here would be permitted to do in order to establish priority. On the other hand, a domestic inventor who is willing to dedicate his invention to the public may be held as an infringer by reason of the later patenting of an invention abroad which antedates the invention and use in this country; and so is put in a worse position vis a vis a foreign inventor who subsequently secures a patent, and succeeds in establishing an earlier date of invention, than he would occupy if he had promoted his own interest by procuring a patent.

We have no way of knowing whether the discrimination results from inadvertence or from some undisclosed legislative policy, but, in order to redress the disadvantage under which one in the petitioner's situation suffers, we should have to read into the law words which plainly are missing.
16
We cannot thus rewrite the statute.
17
Moreover, Sections 4886 and 4887 have repeatedly been amended and other portions of the patent act have been revised and amended from time to time since the decisions pointing out that Section 4886 did not prevent the foreign inventor from carrying back his date of invention beyond the date of his application. Congress has not seen fit to amend the statute in this respect and we must assume that it has been satisfied with, and adopted, the construction given to its enactment by the courts.
18
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We are of opinion that the courts below were right in not limiting Shimadzu's date of invention to the date of his application but allowing him to show an earlier actual date.

Second. A patent is not validly issued if the invention 'is proved to have been abandoned.'19 Abandonment may be evidenced by the express and voluntary declaration of the inventor;20 it may be inferred from negligence or unexplained delay in making application for patent;21 it may be declared as a consequence of the inventor's concealing his invention and delaying application for patent in an endeavor to extend the term of the patent protection beyond the period fixed by the statute.
22
In any case, the question whether the invention has been abandoned is one of fact.